The longitudinal decline in lung function in swine barn workers has been linked to air con-taminants [22] and a dose-response relationship exists between decline in lung function and end
Trang 1and Toxicology
Open Access
Review
Pulmonary effects of exposure to pig barn air
Chandrashekhar Charavaryamath and Baljit Singh*
Address: Department of Veterinary Biomedical Sciences and Immunology Research Group, University of Saskatchewan, Saskatoon, SK S7N 5B4, Canada
Email: Chandrashekhar Charavaryamath - c.chandru@usask.ca; Baljit Singh* - baljit.singh@usask.ca
* Corresponding author
Abstract
Swine production has undergone rapid transformation from family owned operation to a large scale
industrial enterprise Since increasing number of pigs are reared on a large scale in confined
buildings, some of the swine barn workers may be employed to work eight hours per day Swine
barn workers suffer from higher incidences of impaired air flow and lung inflammation, which is
attributed to high intensity and interrupted exposures to pig barn air The air in these barns
contains gases, dust, microbes and endotoxin with endotoxin being the major suspect as the cause
of lung dysfunction This review attempts to describe the current state of knowledge of incidences
and mechanisms of pulmonary dysfunction following exposure to the barn air
Changing face of pig industry in Canada
Canada is among the top five pork exporters of the world
with a total pork export of 970,000 tons in the year 2004,
which translates into cash receipts of $4.2 billion in the
year 2004 representing a 25% increase over the year 2003
In 2005, Canada had 14.9 million hogs which is an
increase of 1.7% over the previous year and the pork
export is expected to grow by 2% [1,2] Currently, pork
sector accounts for 30% of total livestock shipments and
for 10% of all farm cash receipts in Canadian farm
econ-omy Further, swine farming has provided employment to
10,790 people in Canada [3] Therefore, swine
produc-tion is a major component of Canada's agricultural
econ-omy Although the number of pigs has increased but the
number of farms has shown a decline to indicate fewer
people are working longer shifts on the farms Now a
days, small family operated pig farms are making way for
large scale facilities where thousands of pigs are raised in
a single facility [4] Large pig production operations
require many full time workers who work 8 hour/day and
5 days/week and thus experience high intensity
inter-rupted exposures to the barn air [5,6] However, still many workers may work only a few hours every day inside a pig barn The barn air is very complex and contains organic dust, plant materials (pollen grains, feed grains, hay and silage), animal origin materials (swine dander, hair, urine and pig proteins), microbial components (mite or their parts, bacteria, endotoxin, (1–3) β-D-glucan and fungal spores) and a number of gases such as ammonia, carbon dioxide, hydrogen sulphide and methane [7-9] Therefore, although modern barns appear cleaner, the air inside these barns still carries toxic molecules which are harmful
to the workers [10]
Clinical symptoms
Exposure to the toxic molecules in the barn air is a risk fac-tor for the development of chronic respirafac-tory symptoms and lung dysfunction [11] Respiratory diseases in agricul-tural farmers are one of the earliest recognized occupa-tional hazards [12] Among the agriculture workers, swine farmers report higher prevalence of occupational respira-tory symptoms than in other farmers [13] Exposed
work-Published: 06 June 2006
Journal of Occupational Medicine and Toxicology 2006, 1:10 doi:10.1186/1745-6673-1-10
Received: 06 February 2006 Accepted: 06 June 2006 This article is available from: http://www.occup-med.com/content/1/1/10
© 2006 Charavaryamath and Singh; licensee BioMed Central Ltd.
This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/2.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
Trang 2ers report significantly higher frequencies of respiratory
symptoms, chest illness, cold and pneumonia [7,14] The
severity of respiratory symptoms in the workers increases
during the winter due to the reduced ventilation and is
also related to the number of working hours [15]
Previous studies have recorded reductions in expired flow
rates in barn workers [11][16-19] Further, barn workers
also exhibit increased airway responsiveness and airway
inflammation [20,21] The longitudinal decline in lung
function in swine barn workers has been linked to air
con-taminants [22] and a dose-response relationship exists
between decline in lung function and endotoxin and
ammonia levels in the barn air [17] Exposure to the barn
organic dust causes airway inflammation and increased
airway resistance both in humans and animal models
apart from contributing to the exacerbation of asthma
[23-27] These observations show that the barn air
con-tains toxic molecules which induce lung dysfunction in
pig barn workers
Effects of acute single exposure to the swine
barn air: human studies
To better understand the negative effects of exposure to
swine barn air, many researchers have exposed nạve,
healthy volunteers to the swine barn air for a short period
of time (2–5 hours, once) This study model mimics the
lung response of new workers following first exposure to
the swine barn air Single two-five hours of exposure of
nạve, healthy volunteers to swine barn air is shown to
induce bronchial responsiveness [28], fever, malaise and
drowsiness [21] Across the shift change in lung function
during exposure is an important predictor of longitudinal
changes in lung function in swine confinement workers
[29] Further, a 75-fold increase in neutrophils, a
two-three fold increase in mononuclear cells and a significant
increase in eosinophils, fibronectin and albumin levels in
bronchoalveolar lavage fluid (BALF) [21] and levels of
IL-1β, IL-1 receptor antagonist, IL-6 and TNF-α increased in
the serum of the exposed nạve volunteers The changes in
IL-1 receptor antagonist levels correlated with changes in
FEV1, bronchial responsiveness, oral temperature and
white blood cell count while IL-1β levels correlated with
oral temperature [30] Further, it is shown that, a single
exposure to barn air also caused thickening of nasal
mucosa, increased numbers of neutrophils in nasal lavage
and BALF, increased numbers of macrophages,
lym-phocytes, eosinophils and the levels of IL-8 in the BALF
[31,10] Interestingly, levels of IL-8, a potent
chemoat-tractant for neutrophils, correlated with increase in
neu-trophils in the nasal lavage fluid [31] It is obvious that
single exposure to the barn air can activate an
inflamma-tory response in human lungs
Animal exposure studies
Although data from studies involving human volunteers has shown induction of lung inflammation following exposure to the barn air, animal studies are critically needed to better understand cell and molecular changes
So far, there have been very few animal model studies to map the mechanisms of barn air-induced lung dysfunc-tion For example, rabbits and guinea pigs maintained for
12 months in a confined nursery-grower unit showed dif-fuse interstitial histiocytic pneumonia, epithelial hyper-plasia and metahyper-plasia of tracheal and nasal turbinates, with sub mucosal infiltration of plasma cells and heter-ophils [32] Interestingly, blood from these test animals contained serum precipitins to dust extract from the swine confinement building [32]
To mimic the work schedule at modern pig barns, we exposed Sprague-Dawley rats to pig barn air for a period
of 8 hours/day for one day, 5 days or 20 days The expo-sures were interrupted for 2 days after each 5 days of 8 hour/day exposure and rats were kept in clean air during this interruption Rats exposed to the swine barn air for one or five times showed increase in airway hyperrespon-siveness compared to those exposed 20 times or controls Lungs from all the three exposed groups (one, five and 20 day) were inflamed with recruitment of neutrophils and eosinophils in five and 20 day exposed groups [33] These responses are similar to those observed in human volun-teers exposed to the barn air for 3–5 hours [28,34,35] Interestingly, airway reactivity in rats following 20 expo-sures was not different compared to the controls to sug-gest physiological adaptation to the pig barn air Similarly, following single exposure to the barn air, swine farmers only show minor alterations compared to nạve volunteers to suggests adaptation [36,37] It is possible that adaptation in animal models may be induced follow-ing exposures shorter than 8 hours
Because we found high concentrations of endotoxin in the barn air, it may be central protagonist in initiating lung inflammation in the exposed animals These data show that rat lung responses to the barn air are similar to those
in humans and that rat may be a reliable model to simu-late lung dysfunction in humans following exposure to the barn air [33]
In vitro studies on the effects of swine barn dust
Several researchers have shown the inflammatory
poten-tial of swine barn dust or air in many in vitro experiments
[38-40] These in vitro studies are a valuable tool to under-stand the effects of swine barn air or dust on a variety of lung cells These studies provide an opportunity to control various variables to facilitate identification of cellular and molecular pathways that regulate response to swine barn air Swine dust induces release of IL-8 in normal human
Trang 3bronchial epithelial cells, human pulmonary epithelial
carcinoma cell line (A549) and in human alveolar
macro-phages [38] Swine dust is almost as potent as
lipopolysac-charides in stimulating cytokine release from alveolar
macrophages in vitro [39] Recent data showed that swine
barn dust activates protein kinase C to induce secretion of
IL-8 and IL-6 from airway epithelial cells and promotes
adhesion of lymphocytes through upregulation of
ICAM-1 [40,4ICAM-1] Swine barn dust can also directly activate
T-lym-phocytes [42] These data show importance of performing
in vitro studies along with human and experimental
ani-mal investigations to further our understanding of lung
responses to pig barn air
Conclusion and future studies
The data from animal and human studies show that barn
air can induce lung dysfunction Recent data from animal
studies and from in vitro studies have started to elucidate
mechanisms of lung dysfunction induced following
expo-sure to the barn air However, many questions remain
unanswered One of the central questions relates to
pre-cise and relative contributions of various toxic molecules
in the barn air to lung dysfunction The endotoxin is the
foremost toxic agent in the barn air The role of endotoxin
in barn air induced lung dysfunction can be assessed
through the use of mice that lack a functional Toll-like
receptor-4 Second logical experiment is the physical and
biochemical characterization of the dust particles in the
barn air Specifically, we need to know if the barn air
con-tains dust particles which are less then 100 nm in size
because particles of this size are believed to provoke a
vig-orous cardiopulmonary response [43,44] The
biochemi-cal characterization of the particles would reveal if
particles are used as Trojan horse to carry endotoxins and
other toxic molecules into the lungs
Competing interests
The authors declare that they have no competing interests
Authors' contributions
Both the authors contributed equally in the preparation of
this review
Acknowledgements
The work done in the authors' laboratory was supported through grants
from Saskatchewan Lung Association and Natural Sciences and Engineering
Research Council of Canada to Dr Singh Dr Charavaryamath is supported
through Graduate Merit Scholarship from University of Saskatchewan
(2002–2004) and a scholarship from the CIHR Strategic Training Program
in Public Health and the Agricultural Rural Ecosystem (PHARE) and Partner
Institutes including the Institute of Cancer Research, Institute of
Circula-tory and RespiraCircula-tory Health, Institute of Infection and Immunity, Institute
of Population and Public Health and the University of Saskatchewan We
regret that due to space constraints we may not have cited a few worthy
publications.
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